NI 9485 Circuit Issue

[Paul_Knight_Lockheed_Mart]

I have an issue with an NI-9485.  I am trying to us it to turn on a High Voltage AC relay.  I have the +24V need to run the HV relay to CH0a.  CH0b is connected to the positive of the HV relay's coil.  The negative of the HV relay' coil is connected to ground.  When I turn on the +24 Volts, no matter what the state NI-9485 I get 10mA of current that turns on the HV relay.

If I remove the connection to the NI-9485 and hook up on ohm meter to it, the relay works fine.  If I replace the NI-9485 with a NI-9481 the current only flow when the NI-9481 is commanded closed.  NI-9485 was picked because of the channel count.

Does anyone know why the NI-9485 does not like to switch +24V?

[esoDerek]

Hey Paul,

I'm not an expert in relays but I'll help how I can. Without knowing more about your setup, I'd first refer you to the wiring diagrams for the 9485 - be sure to review your setup and make sure your HV relay is connected correctly. Is your load inductive? You may need to add an MOV (see Page 10 in the manual below): 

http://www.ni.com/pdf/manuals/374820c.pdf#page=9

Also check the specifications and make sure that your voltage and/or current do not exceed the limit for a given channel:

http://www.ni.com/pdf/manuals/374820c.pdf#page=13

Since SSRs use semiconductors, there can be reverse leakage current, which might explain the 10mA current present even while the NI-9485 is in the open state... Although the reverse leakage current is usually smaller than 10mA...

Can I ask you to expand a little on your setup? You're activating a HV relay using your solid state relay? Or am I getting that wrong? 

[Paul_Knight_Lockheed_Mart]

After more testing it appears that Ch0 is bad.  Replacing the module with a different one the circuit started to work.

[esoDerek · Accepted solution]

Glad it worked!

Have a great afternoon.